Electrochemical devices, such as batteries and fuel cells, typically incorporate an electrolyte source to provide the anions or cations necessary to produce an electrochemical reaction. Batteries and fuel cells operate on electrochemical reaction of metal/air, metal/halide, metal/hydride, hydrogen/air, or other materials capable of electrochemical reaction. A lithium (Li)/air system, for example, requires the diffusion of oxygen gas in the cathode, and typically will incorporate an organic solution as the electrolyte. The lifetime of this battery is however, limited for several reasons. First, the naked Li anode is corroded by both the moisture that is entrained into the cathode with oxygen from ambient air and leaked through the separator. Second, the oxygen and Li(+1) ion paths of the cathode gradually become blocked due to reaction of the Li(+1) with the moisture impurity. Third, the electrolyte solution becomes lost into the ambient air due to vaporization. In addition to the Li/air systems, other metal/air systems, such as aluminum/air, Zn/air, cadmium/air, magnesium/air, and iron/air systems, also have the potential for many different applications due to their theoretically high ampere-hour capacity, voltage, and specific energy, but these systems are also plagued by corrosion of the anode caused by the moisture coming from ambient air
Conventional membranes are often comprised, in part, of polymeric or ceramic materials. Such conventional membranes have many associated deficiencies such as low selectivity and/or relatively high cost.
Immobilized liquid membranes (ILMs) contain a liquid solution immobilized in the pores of a matrix, by physical forces. The liquid solution includes a carrier that absorbs/desorbs reversibly with the gas species of interest. ILMs can potentially provide the highest fluxes and selectivities for reacting species such as oxygen. However, commercialization of these membranes as selective barriers in electrochemical devices has not taken place due to the limitation of stability of conventional liquid membranes.
Multiple factors contribute to the instability of available ILMs. First, instability is caused by the absence of any chemical bonding of the carrier to the matrix. Evaporation of the carrier and/or the liquid solution into gas phases during the operation also contributes to ILM instability. Moreover, instability is caused by lower breakthrough pressures associated with the liquids and the inability of the membranes to withstand even temporary oscillations in humidity conditions on either side of the liquid membranes.